In recent years, mobile terminal devices such as smartphones generally have a function that is able to provide a so-called locked state that restricts entry operation when there has been no operation for a predetermined period of time and to release the lock upon personal authentication when entry operation is started. This function allows for prevention of information leakage to a third party, because the mobile terminal device may not be used unless the personal authentication is successful. As a method of personal authentication, there are known methods involving entry of a personal identification number or a password and methods involving biological information such as a fingerprint, a face, an iris, a retina, a vein, a palm shape, DNA, a voice, a signature, an auricular, or the like, for example.
Further, as a technique that can omit entry operation for personal authentication, Japanese Laid-open Patent Publication No. 2014-123204 discusses a method of performing personal authentication by using an equipped wearable device. This is a technique in which a wearable device and a mobile terminal device have been set in advance to be able to communicate with each other by Bluetooth (registered trademark), and the mobile terminal device can be unlocked when the wearable device is located near the mobile terminal device and the communication by Bluetooth is established.
As another technique that can omit entry operation, Chuong H Nguyen, “Personal Unlocking makes security simple in Android L”, Internet website, URL: http://www.androidcentral.com/personal-unlocking-makes-security-simple, searched on Jan. 29, 2015, online, discusses a technique in which, after mutual authentication between a smartphone and a wrist-watch-type wrist terminal, a user performs an unlocking operation on the wrist terminal, and the wrist terminal then transmits an unlocking command to the smartphone.
According to the technique disclosed in Japanese Laid-open Patent Publication No. 2014-123204, however, a third party is able to unlock a smartphone when the wearable device is located near the smartphone. For example, it is assumed that a user is wearing a wearable device and a third party places a user's smartphone in a location such as a neighboring room where mutual communication by Bluetooth is available but which is out of sight of the user. In this case, the third party is able to unlock the smartphone.
According to Chuong H Nguyen, “Personal Unlocking makes security simple in Android L”, although entry operation at the smartphone side for releasing the lock is unnecessary, entry operation at the wearable device side is still involved. In view of the techniques discussed above, a simpler unlocking operation with high security is desirable in an information processing device such as a mobile terminal device.